Safe tap water is gushing again from taps and shower heads in West Virginia, a welcome sight and sound for a small fraction of the 300,000 people who have not been able to use running water since a chemical spill five days ago.

It could still be days before everyone in the Charleston metropolitan area is cleared to use the water, though US officials said the water in certain designated areas was safe to drink and wash with as long as people flushed out their systems.

They cautioned that the water may still have a slight licorice-type odor to it, raising the anxieties of some who believed it was still contaminated.

"I'm not going to drink it. I'll shower in it and do dishes in it. But I won't drink it. I don't think it's (the chemical) all out," said Angela Stone, who started the 30-minute or so process of flushing her system out soon after the ban was lifted.

By Monday afternoon (local time), officials had given the green light to about 10 per cent of West Virginia American Water's customers, and company spokeswoman Laura Jordan said as much as 25 per cent of its customer base could have water by the end of the day.

The water crisis shuttered schools, restaurants and day-care centers and truckloads of water had to be brought in from out of state. People were told to use the water only to flush their toilets.

Officials were lifting the ban in a strict, methodical manner to help ensure the water system was not overwhelmed by excessive demand, which could cause more water quality and service problems. A

n online map detailing what areas were cleared showed a very small portion in blue and a vast area across nine counties still in the "do not use" red.

Customers were credited with 3,785 litres of water, which was likely more than enough to flush out a system. The average residential customer uses about 12,500 litres per month.

The first area cleared was downtown Charleston, the state capital and its largest city. Hospitals were flushing out systems as were schools, which hoped to open again.

The water crisis started last week when a chemical used in coal processing leaked from a Freedom Industries plant into the nearby Elk River.

In all, state officials believe about 28,390 litres leaked from the tank. Some of the chemical was contained before flowing into the river and it's not clear exactly how much entered the water supply.

Federal authorities, including the US Chemical Safety Board, have opened an investigation.

Over the past few days, tests have showed that levels were consistently below a toxic threshold, and in some samples, there was no trace of the chemical at all.